This Phase 2A study is an adaptive design pilot study investigating the efficacy and safety of daily Acthar administration in diabetic patients with nephropathy and proteinuria. Patients with type 1 diabetes mellitus (T1DM) or T2DM who currently take insulin will be enrolled and randomized into 6 study groups and will be treated with either Acthar or Placebo for 36 weeks, followed by a 4 week dose taper, and a 12 week observation period. The study will compare three dose regimens of Acthar (8 U [0.1 mL], 16 U [0.2 mL], and 32 U [0.4 mL]) to equivalent volumes of Placebo to ensure the double-blind nature of the study.